Method for high vacuum fractional



p 1940; a. K. VON ELBE ET AL 2.198.84

METHOD FOR HIGH VACUUM FRACTIONAL DI STILLATION Filed June 29, 19:56 2 Sheets-Sheet 1 fl/srlzz/lvq 705E April 30, 1940. a. J. K. VONELB E ET AL METHOD FOR HIGH VACUUM FRACTIONAL DISTILLATION b Q q I I Mk m K NVENTORS QNW KmvQQXN Kati b Mm A... 30', 1940 2,198,848 8 METHOD FOR HIGH VACUUM FRACTION DISTILLATION Guenther J. K. von Elbe and Benjamin B. Scott, Jr., Pittsburgh, Pa., assignors to Carnegie Institute of Technology of Pittsburgh, Pittsburgh, Pa., a corporation oi Pennsylvania Application June 29. 1936, Serial No. 87,914

7 Claims. (Cl. 202-52) Our invention relates to the separation of the components of a mixture and is particularly applicable to fractional distillation in a high vacuum with complete recovery of the material being 5 fractionated; i. e. without holdup in the column. The term fractional distillation as herein employed is meant to include what is ordinarily known as distillation and sublimation.

Both in laboratory work and in commercial l practice, separation of the components of a mixmixture and to obtain much more satisfactory ture is commonly obtained by fractional distilresults than have hitherto been possible. Morelation. Efiective fractionationin apparatus using over, a very small sample ranging from 0.001 c. c. a conventional column requires a distillation rate to 0.1 c. c. will suflice, although larger amounts suflicient to maintain a certain volume of liquid may be used, and the components thereof can in the column and a high reflux ratio. This I be sharply separated and completely recovered.

condition limits the use of such a column to tem- Our method'and apparatus, may be used at temperatures above that at which the vapor presperatures above or below room temperatures desure of the mixture is about one millimeter prespending on the characteristics of the mixture to sure of mercury. Since the fractionation or be fractionated and with mixtures, the compo- 3 fractional distillation depends on repeated connents of which have boiling points which are densation and re-evaporation along the tempera close to one another. ture gradient maintained in the column, a certain We have invented suitable apparatus for carryvolume of liquid is necessarily continuously held ing out our invention, which apparatus we shall in the column. This hold-up of the column 1 hereafter describe and by which we are able to e 5 normally limits the minimum size, of the sample obtain separation of the components of the mix- 85 to be used so that from 2 to 4 c. c. is required. ture in a highly satisfactory manner, due to their Though it is possible to distill smaller samples diflerence in vapor pressures. Our apparatus is at vapor pressures lower than one millimeter of Such that we can maintain a suitable (exceedmercury, nevertheless, at very low pressures, such ingly constant) temperature gradient through m as are used in a molecular still--which may be which the sample may be moved to accomplish 80 defined as a still operated at a pressure such fractional distillation thereof. that the distance from the evaporating surface The sample is placed in a tube within the apto the condensing surface is less than the mean paratus under vacuum in such a manner that free path of the vaporized molecules-it has been two spaced apart or related units, acting as 5 found that the individual components each disheater and cooler, respectively, with the aid of till at a rate proportional to their partial vapor the necessary temperature control and motion pressures, so that separation of a pure component control devices, cause distillation of the volatile i not possible without repeated distillations components of the mixture under the influence equivalent to the condensation and re-evaporaof the temperature conditions" and vacuum from 0 tion occurring in the conventional column. Vacthat section called the heater zone to'that called 40 uum distillation, we have discovered, has the adthe cooler zone. The more volatile components vantage of permitting operation at lower temwill distill more rapidly than the-less volatile. peratures where the relative differences in vapor It is to be understood that heater and cooler, pressures of the components may be greater and as well as heater zone or hot zone, and cooler 5 at temperatures below that at which thermal dezone or cold zone, are terms representing that '45 composition takes place. We have discovered the heater or heater zone and cooler or cooler that by a proper utilization of the behavior of zone are run at relatively diii'erent temperasubstances due to the diflerences in their vapor tures-.-'I'he heater or heater zone may be run pressures at certain temperatures, it is possible at a temperature above or below room tempera- 0 to separate the components of a mixture in such tures and the cooler or-cooler zone may be run so a manner that such components may be of a at a temperature above or below room temperapurity which has hitherto been impossible to tures. It will also be understood that the heater .or heater zone will always be run at a tempera- By the use of our invention, it is possible-to ture higher than the cooler or cooler zone. The 5 fractionally distill very small samples ranging temperature gradient so formed is such that displete recovery of the material being fractionated and wherein there is substantially no "hold up" in the distilling tube. We are thus enabled to readily separate individual components from a tillation takes place at temperatures at which the difference in vapor pressures of the components of the material to be separated is of an order sufficient to allow appreciable fractionation.

In order to produce separation of the commoved with the cooler advancing towards the sample. The movement of the sample relative to the temperature gradient between the heater and cooler causes repeated fractionation of the material and separation to take place in such a manner that each component forms a separate band of material along the distilling tube. When separation has been movement of the tube. with the aid of automatic pulling devices allows the products to be: moved towards the end for removal and the temperature of the heater or the pulling speed or both is adjusted so that the least volatile constituent of the mixture will become or remain unvaporized as a component band in the heating zone. This component can be removed in various ways as will later be described.

Due to the pressure gradient within the distilling tube. along the temperature gradient, the vapor of the'more volatile components tends to be swept away from the warm to the cool end. For this reason, the less volatile component is obtained in a state of great purity.

By our invention, although we accomplish fractional distillation by repeated evaporation and condensation, there is no reflux in the distilling tube. The term reflux is herein used to designate the movement by gravity of a substance, condensed in the distilling tube, from the cold zone of the tube toward the hot zone.

In the accompanying drawings, illustrating a present preferred embodiment of our invention, and in which like numerals are employed to designate like parts, throughout the same;

Figure 1 is a more or less schematic view of one end of an apparatus embodying our invention;

Figure 2 is a schem of'our apparatus;

Figure 3 is a representative temperature gradient;

Figure 4 is a view of a distilling tube at the start of a run on an enlarged vertical scale;

Figure 5 is a view of a distilling tube at the end of a run on an enlarged vertical scale.

The apparatus, see Figure 2, consists in general of two separately controlled, spaced apart thermostatically controlled heat exchangers or thermostats l0 and H, referred to hereinafter as cooler and heater, respectively, connected by a gradient tube l2 and surrounded by a transparent vacuum jacket Hi. The region between the two thermostats has definite temperature characteristics, as will be seen from an inspection of Figure 3. This region between the vertical chain lines of Figure 3 and designated G is referred to as a temperature gradient. Each of the thermostats are alike, each has its own separate temperature control system, and each may be operated at temperatures above or below normal room temperatures, the cooler always at a lower temperature than the heater. The jacket reduces heat losses and prevents condensation of moisture upon the cold parts of the equipment.' Both thermostats and the gradient tic view showing a part completed, control of the follows: The needle valve tube are constructed of copper to allow for rapid heat t ansference. The reduced end portions of the thermostats and the gradient tube have slots ll therein to permit observation of the fractionating process within the glass distilling tube l5 which passes through the axial bore 16 of the thermostats and the gradient tube. A small annular electric heater H is secured to the reduced outer end portion of heater H and is used to facilitate the removal of the separated 'products from the distillation tube l5.

In Figure 1, there is shown a more or less schematic view of one of the thermostats with its associated temperature control apparatus. T represents a thermostat or heat exchanger, M a manometer system, C a fluid container, V a fluid valve and E an electric circuit control system. The thermostat T comprises a round copper bar l8 having an axial passage ii therethrough, a main portion l9, and reduced end portions 20 and 2|, which end portions have slots l4 therein. Formed in this bar isa spiral groove of a small pitch and of a size to accommodate two closely coiled copper heat transfer tubes 22 and 23. The depth and width of this groove is equal to 2D (D, being the diameter of each of the tubes 22 and 23). A spiral groove, of opposite hand, (2D wide by D deep is also formed in the remaining groove sides. Both ends of the main portion of the copper bar are machined to leave narrow cooling chamber end plates 24. The tube 23, containing an insulated resistance wire 25, and the hollow tube 22, are

wound in the grooves formed in the copper bar, and the starts and finishes of both tubes are brought outside through holes in the end plate 24. A thin copper shell 26 is fitted over the coils and together with the tube ends are suitably secured to the end plates by brazing or welding to form a gas and liquid-tight control fluid chamber 21. A length of copper tubing 28 is attached to and passes through the end plate 24 and into fluid chamber 21. Tubes 22 and 23 are placed in the grooves cut into the copper bar for the reason that the remaining metal between the grooves provides more surface for rapid heat transfer through the temperature controlling medium which is introduced into the fluid cham-' ber and results in a faster establishment of a temperature equilibrium throughout the thermostat. The ends of the insulated resistance wires 25 are brought to convenient connector points. One end of tube 22 is connected to container C and the other end of the tube is connected to the electric fluid valve V. Tube 28 is connected to the manometer system M by means of the manometer line or-tube 23.

The manometer'system M consists of a fluid reservoir 30 connected to an upstanding tube 3| of a mercury manometer. The connecting tube 23, which leads from the thermostat, is connected into the passage between the fluid reservoir 30 and the manometer tube 3|. The fluid reservoir 30 communicates with manometer tube 3| by way of a port 32'controlled by a needle valve 33. The fluid chamber or reservoir 30 can be connected to or completely isolated from the to the manometer and thermostat temperature regulating orcontrol fluid chamber 21. The thermostat is adjusted (cooled or heatedifto the predetermined temperature. tlon, enough controlling fluid enters or leaves the thermostat through the manometer line 23 from the reservoir 30 to compensate for the volume changes of the fluid caused by the cooling or heating of it. It is important .in filling the space in the regulating chamber 2'? and connecting tube that all air and gas be removed, because the much greater compressibility, as compared to a liquid, of any gas remaining would produce insensitivity of the temperature control system, since the control is dependent upon the change of pressure produced by expansion and contraction of the control liquid in the chamber 21 with change of temperature. v

After the thermostat has reached the desired operating temperature, which temperature may be ascertained by means of suitably placed thermocoupies, or by other means, the needle valve 33 is closed, thus isolating the reservoir 30 from the manometer system and forcing the manometer to respond to volume changes of the controlling fluid in the thermostat with changes in the temperature. The rise and fall on the mercury column 34 in the manometer makes and breaks the circuit through the manometer fixed contact 35 and adjustable contact 36, which are connected to the control contacts 31 of the electric control system E, thus controlling the heat transfer equipment through the electric control system E and fluid valve V, so that automatic temperature control is obtained. It is apparent that adjustment for temperature control is simply and readily made by use of this arrangement.

The container C contains, when low temperatures are required in the system, a low boiling fluid such as liquid air or liquid nitrogen, and in such case may be the standard metal vacuum flask 38. The flask has a tube 39 which extends djacent to the bottom of the flask and is connected to one end of tube 22. By means of a tube 40, pressure may be applied from a suitable source to the surface of the liquid in the container.

Connected to the other end of the tube 22 is an electric fluid valve V. The fluid valve has a port 4|, which is connected to tube 22.. The opening and closing of the port 4i controls the discharge of the fluid from the tube 22. The port is controlled by needle valve 42 made from magnetic material, which, in turn, is controlledby means of an electric coil or solenoid 43. When the solenoid 43 is energized the needle valve is lifted, and the gas or air pressure in the tube 22 is released through port 4| and heat transfer fluid, for example, liquid nitrogen when a low temperature is desired, is forced from flask 33 through the coil 22, resulting in the cooling of the thermostat T. I

When it is desired to increase the temperature inthe thermostat T, an electric current is caused to flowthrough the resistance wire 25 in tube 23. The flow of current through the fluid valve and through the wire 25 is controlled by means of e the electric control system-E.

"The electric control system E comprises a more or less conventional vacuum tube circuit in which 44 represents the vacuum tube with cathode, plate and grid electrodes. In the plate circuit is a double-acting relay 45 having a condenser 45* shunting its terminals. The plate cathode and ll grid bias voltages are obtained from any suitable During this operasource. a transformer with multiple secondary windings being illustrated at 46. The. transformer 45 furnishes a voltage for the vacuum" tube plate circuit, a medium voltage for the grid bias circuit and a low voltage for the tube filament circuit. It will be observed that the C-bias voltage for the vacuum tube is furnished by a secondary on the power transformer 46. The

relay 45 has an armature 45 which, when the plate current of the tube is flowing, is attracted by the relay to make a contact with contactpoint 45. When the plate current is not flowing. this armature is released, making contact with contact point 45. rent is controlled from the grid, the gridcircuit including wire 41 leading from the cathode of the tube to one of the contact points 31. thence to grid is grounded to the filament, whereupon the,

tube grid is deenergized, and current will flow in the plate circuit to energize relay 45'. Leading to the armature 45 of the relay is a wire connected through a variable resistance 5| to one side of a source of current not shown. The contact 45 of the relay is connected through wire 52 to one end of the winding of the solenoid 43 of the electric fluid valve V. The other end of the winding of the solenoid is connected through The vacuum tube plate curwire 53 to the other side of the current supply circuit. Leading from relay contact 45' is a wire 54 connected to one end of wire 25 'of the thermostat and the other end of wire 25 is connected to wire 53. A switch 55 is interposed in wires 52 and 54 and so arranged that either conductor 52 or 54, but only one at a. time, can be placed in the circuit from the relay to the solenoid 43 or to heater-wires 25. p

Operation of the system v The thermostats and their associated control apparatus are assembled as shown in Figure 2,.

' ation of a mixture of para and meta xylene,

which components cannot be separated by hitherto known methods of fractional distillation. It will be observed that the temperatures of the cooler and heater,'respectively, are diiierent and these temperatures which may be varied during the run are determined beforehand by experiment. The method of obtaining and holding the required temperature is the same for both thermostats so thata description of the operation of one thermostat will be equally applicable to the operation of the other thermostat, since they are similar in. construction. It will be also understood that by means of this apparatus any, desired temperature may be indefinitely maintained in either thermostat, and our invention is not thermostat warms slightly (due to heat trans-' limited to low temperatures nor to any particular-mixtures. It is essential that the external atmosphere about the distilling tube be maintained above the temperature of theheater.

We shall now describe the operation of the apparatus when it is desired to fractionally distill a typical mixture, for example, of para and meta xylenes. It is extremely difllcult to separate these two substances by hitherto known methods of distillation, since their boiling points at atmospheric pressure'are almost identical (138 C. and 138 C., respectively); By the use of our invention, the separation can be readily accomplished and the substances obtained in a high state of pu y.

After the apparatus is assembled. the control fluid chamber 21, reservoir 30, and the tubes con.- necting the chamber and reservoir are fllled with a suitable control fluid, in this case toluene, care being observed that all air and gas be removed from the system as heretofore described. The needle valve 33 is unscrewed, thus connecting the reservoir 30 to the manometer system and to fluid chamber 21. -Air at a pressure of from 2 to 5 lbs. per sq. in. is applied by way of tube Ml to the surface of the liquid nitrogen in flask 38. Since the port 4| of the fluid valve V is closed, suflicient nitrogen will evaporate to produce pressure equalization in the liquid nitrogen container and the thermostat heat transfer coil 22. The control contacts 31 of electric control system E are short circuited, the tube grid deenergized and current flows in the vacuum tube plate circuit, energizing the relay 45 and current flows through wire 50, armature 45*, contact 45, wire 52, and solenoid 43. Valve 42 is lifted from port 4| and the evaporated nitrogen passes to the atmosphere. The back pressure of nitrogen gas in the thermostat being released through the air valve, causes more liquid nitrogen to be forced into the coils 22 where it evaporates and produces cooling. As the thermostat cools, the volume of toluene control fluid in chamber 21 contracts and the deficiency is replaced by toluene from the reservoir 30. When the thermostat has been cooled to the desired predetermined temperature, which may be determined by means of thermocouples or otherwise, the external short circuit is removed from the contacts 31 causing the vacuum tube relay to become inoperative and resulting in the closing of port 4| of the fluid valve V. Once again, back pressure is built up in the thermostat and any remaining liquid nitrogen is forced back into the container 0. (The excess pressure necessary for this is produced by the rapid evaporation in a relatively warm confined space of part of the remaining liquid nitrogen.) The port 32 is then closed by needle valve 33, thus hydraulically connecting the manometer to chamber 21 and isolating the reservoir 33 from the system. Contact 36 is adjusted with reference to the mercury column 34, so that the contact therebetween is just broken. As soonas the fer by conduction along the gradient tube, convection at the thermostat ends, and radiation all over), the toluene control liquid expands and ,,forces the mercury column 34 upwardly and makes contact with contact 35, thus closing the manometer relay ,control circuit contacts- 31. When the thermostat again cools to the previously set controlling temperature, the control liquid contracts in volume and the manometer contacts 35 and 36 are open-circuited and the coolingstoppage process-is repeated. The thermostat temperature is thenceforth automatically maintube relays are disconnected from their respective power supplies. This cooling system results in trouble-free'automatic temperature control of the thermostats to at least within plus or minus 0.03 C. at temperatures almost to the freezing point (approximately -l10' C.) of the toluene temperature control fluid. Control at temperatures lower than this can readily be obtained by the use of a control fluid having a lower freezing point than toluene.

If it is desired to operate the thermostat above room temperatures, the wires 25 of electric heater 23 are connected in place of the fluid valve V, and

the container C is disconnected from the system. Power flows through contact 45 to the heater wires 25 when the connectors 35, 36 of the manometer is broken, which occurs when the temperature of the thermostat falls. Otherwise, the operation of the temperature control system is the same as for cooling.- If desired, temperatures above room temperatures may be maintained by substituting for theliquid nitrogen in flash 38, a heating medium such as hot oil or gases, in which case the current to operate the fluid valve V will be supplied through contact '45. The material to be fractionated which may be as small as 0.001 g. is placed in a thin walled glass sampling tube, all air is removed therefrom, and the tube sealed off. Free space in the sampling tube is kept at a minimum, so that it may be broken by the expansion of the material upon being gently heated. This tube and sample is placed in and adjacent to one end of the distilling tube l5, whichis then pumped out to a pressure of the order of 2x10 mm. of mercury and the tube sealed ofl. The temperatures of the cooler l0 and heater H are adjusted to experimentally determined values. Because of the difference in temperature between the cooler l0 and heater H, a temperature gradient G (see Figure 3) is present in the cooler-to-heater gradient tube l2, which in a short-time assumes a.

steady condition. The distilling tube I5 is placed in the bore IQ of the apparatus and attached to a device (not illustrated) beyond the electric which device also keeps slowly turning the tube l5. After the distilling tube has come to a temperature equilibrium with the thermostats Ill and H and connecting gradient tube l2, the portion of tube l5' surrounding the material-filled sample tube is gently heated until the sample tube is broken by the e p nding liquid. Sufllcient time is allowed for all the material undergoing fractionation to distill into the gradient, beforethe pulling and turning of distilling tube I5 is begun. It will be observed that the pressure in tube ii, if the tube were allowed to stand for an indefinite period, would be equal to the sum of the partial pressures of the substances comprising the mixture at the temperature corresponding to the temperature of the coldest part of the tube, and there would be a migration of the molecules toward the coldest part of the tube, so that in time the material would collect there. However, moving the tube at the proper speed inside the tube between the heater and cooler. A

proper selection of the pulling speed 01' the tube will cause the components to distill and separate and the components will collect in separate bands., The appearance of the material at the start of a run is shown by I I of Figure 4, which shows the mixture which has distilled from the warm toward the cold end of tube II and adhering thereto in a thin crystal and/or liquid layer (when para and meta xylene are being fractionated) The tube is then turned and pulled at a speed so that the most volatile component will stay in the gradient near the cold end but the less volatile components will nothave time to migrate to the cold end. The forward movement of the tube from the cooler toward the heater will cause the materialto be repeatedly distilled, condensed, and separated into its components, each of which will form a'separate band along the distilling tube. When the band of the least volatile component is moved into the even temperature zone of the heater and of the gradient, as observed through the slot H, the pulling speed of tube I5 is increased. When the least volatile component band has nearly reached the outside end of the heater, it is of a high degree of purity, and it is time to remove it. The enlarged drawing of the distilling tube ii, of Figure 5, shows at I! and I! the appearance of the mixture components at the end of a fractionation, when the volatile mixture is composed of but two substances, e. g. meta and para xylene.

Either of two methods may be used to remove the fractions as they are separated.

In the first method, the temperature of the heater II is lowered to that of the cooler I. Since there is no longer a temperature gradient existing between the heater II and cooler It, distillation stops, and the mixture components remain in a fixed position in the distilling tube 15,

pulled out of the the distilling tube is quickly apparatus until the section containing the first fractionation is beyond the outside end of heater II. The distilling tube It is then heated with a hot flame at a point between the-first fraction and the remainder of the material undergoing fractionation until the tube wall collapses, thereby isolating the first fraction. The distilling tube is then pushed back into its former position in the apparatus, and the temperature gradient is re-established and theprocess is resumed. Ii all of the least volatile components has not been removed, the distillation process is repeated-until all of the least volatile component has been re- 1 moved. It is easy'to determine whether or not I all of the least volatile component has been reband in the section of the distilling tube in the moved, because with the proper adjustment of heater and cooler temperatures and pulling speed, each component forms a separate, distinct gradient, which may be observed through slot II.

In certain cases of extremely volatile substances where sufllciently low temperatures cannot be conveniently obtained in the cooler it, we have found that it is'advantageous to pack the distilling tube I 5 with glass beads, since thereby a greater surface is oilered'for the condensation of the material and its progress to the coldest portion of the distilling tube is greatly retarded.

The second method of removing the separated productsconsists in lowering the temperatures of the heater and of the cooler until there is substantlally no vapor pressure. A liquid air trap and a pump (not shown) are connected to the heater end of the distilling tube l5, and a small leak is connected. to the cooler end of the distilling tube through which dry air may be passed. The heater I l is connected to a. power supply and brought to a temperature suitable for vaporizing the least volatile is begun and the first fractionation of material is slowly brought into the zone of the electric heater I1. As the substance is vvaporized, it is swept out of'the distilling tube l5 by the air and is collected in a suitable trap. After the first fraction has been taken out, the leak is removed, the tube is again sealed, the distilling tube is re-evacuated, and the process is repeated.

In the case of a binary mixture, the least volatile substance is first removed as described. The material is again distilled, and, if all of the least volatile component has not been removed, it may be necessary to continue the process even further, but it is tobe noted that the least volatile substance obtained is of an gree of purity. Our invention, of course, is not limited to binary mixtures but mixtures having more than two substances may likewise be fractionated, each of the volatile substances remaining in the mixture beingtaken on in succession in inverse ratio to their volatilities. v

The following is a non-limiting example of a typical application of our invention. In this case para and meta xylenes were fractioned. These' two substances are extremely diflicult to separate by hitherto known methods, due to their closely similar physical characteristics! Their boiling points at atmospheric pressures are almost identical, 139 C. and 138 0., respectively, Visual observation of the separation process was facilitated by the fact that p-xylene, which has a melting point of 13.2 0., is crystalline, and m-xylene, having a melting point of 51 C. remains liquid under the proper conditions of gradient and pulling speed for producing fractionation. The p-xylene, being the least volatile, is removed first from the distilling tube at the completion of the process. The following temperatures and pulling speeds were found to be effective in the separationof these xylenes.

Ortho-nitro toluene and para-nitro toluene were fractionated successfully. The boiling pointr of the first is 220 C. and the point of the,

second is 237 C. The melting point of ortho is --10.5 0., and the melting point of para is 51 C. At the beginning of the run, the cooler temperature was --20 C. and the heater temperature was 25 C. A suitable pulling speed was 1 cm. per minute.

By our invention, it is possible to control thetemperatures of the heater and cooler and, consequently, the slope of the gradient within extremely close limits. It is possible to control the temperature of theheater andthecooler within 0.03 C., and the materials separated are of a purity which so far as known tests are concerned is absolute.

While we have illustrated and described a preferred embodiment of our invention, it will be understood that the invention is not limited thereto, but may be otherwise embodied and practiced fractionation. Pumping extremely high de.-

2. The method of fractional distillation of amixture the components of which have different vapor pressures under the conditions of operation which consists of introducing the mixture into an-evacuated elongated sealed container and passing the container substantially longitudinally through a controlled temperature gradient from the cold zone toward the hot zone, at such a speed that the components of the mixture will repeatedly distill and separate into bands in the container along the gradient, the band of the least volatile component being nearest the higher temperature end of the gradient.-

3. Themethod of fractional distillation of a mixture, the components of which have different vapor pressures under the conditions of operation whichconsists in introducing the mixture into a sealed elongated distilling tube having a high degree of vacuum, introducing said distilling tube into a space connecting a cold zone and a hot zone, and causing relative longitudinal movement between the tube and the space at such a speed that the components of the mixture will repeatedly distil and condense and while in the vapor phase will move from the hot zone toward the cold zone until the components are physically separated into sections along the container, removing the container from the gradient and separating the sections.

4. In the method of fractional distillation of a mixture the components of which have'diiferent vapor pressures, the steps comprising partly filling an elongated container with the mixture,

sealing the container and passing the container longitudinally through an elongated passage provided with heated and cooled zones between which a temperature gradient is established, the

temperature in the gradient being suchthat the difference of the vapor pressure of the components is sufficient to cause fractionation by re-- peated evaporation and condensation of the par-#- ticles along the container until the components are physically separated into sections along the container, removing the container from the apparatus and separating the sections.

5. The method of fractional distillation of a mixture of solids or liquids which have different vapor pressures under the conditions of operatherein the mixture, longitudinally through anincreasing temperature gradient from the cold end to the hot end, the upper limit of the gradient and speed of passage of the container therealong being such that only the least volatile component can remain unvaporized therein, until at least one of the components of the mixture is separated from the mixture and removing the separated component from the container. I

7. In the method of fractional distillation of a mixture having at least two components of different vapor pressures under the conditions of operation, the steps of introducing the mixture into a highly evacuated elongated sealed container, placing the sealed vacuumized container containing said'mixture in a risingtemperature gradient, the temperatures in the gradient being such thatthe difference of the vapor pressures of the components is sufficient to permit fractionation, moving the container from the cold zone to the hot zone until at least one of the components is separated from the mixture, andremow ing the separated component from the container.

GUEN'I'HER J. K. VON ELBE. BENJAMIN B. SCOTT, Ja. 

